1. Field of the Invention
This invention relates to a joint section between a shaft and universal-joint yoke, and more particularly to a joint in a steering apparatus, for example, that is used for joining the ends of the various shafts of the steering apparatus to a universal-joint yoke.
2. Description of the Related Art
In a steering apparatus for steering the front wheels of an automobile, the movement of the steering shaft that turns as the steering wheel is operated is transmitted to the input shaft of a steering gear by way of cross-shaft type universal joint as shown in FIG. 12. This universal joint 1 joins a pair of yokes 2, 3 by way of a cross shaft 4. The four end sections of this cross shaft 4 are supported on the tip end sections of the yokes 2, 3 by way of bearings that use rollers located inside bearing cups 5 such that they can freely oscillate. Therefore, it is possible to transmit torque between the yokes 2, 3 even though the center axes of these yokes 2, 3 are not on the same straight line.
When this kind of universal joint 1 is installed in a steering apparatus, one of the yokes 2 (right yoke in FIG. 12) is joined and fastened in advance to the end section of one of the shafts 6, such as the steering shaft, by welding or screws, and the other yoke 3 (left yoke in FIG. 12) is joined to the end section of the other shaft 7. Normally, in order to perform this kind of assembly work, after the one shaft 6 is supported by the automobile chassis, this one shaft 6 and the other shaft 7 are joined by the aforementioned universal joint 1.
Also, of the pair of yokes 2, 3 of the universal joint 1, it is preferred that at least one of the yokes 3 is a so-called side-insertion-type yoke (slap yoke) so that connection work can be performed without having to move the one shaft 6 in the axial direction. For example, in the case of the universal joint 1 shown in FIG. 12, the other yoke 3 is a side-insertion-type yoke, while the yoke 2 is joined and fastened to the end section of one of the shaft 6 by welding.
FIG. 13 and FIG. 14 show examples of joints between this kind of side-insertion type yoke 3 and shaft 7, and it is well known prior art as is disclosed in Patent Documents 1 and 2 (JP Patent No. 3,531,364 and U.S. Pat. No. 4,900,178). The base-end section 8 of the yoke 3 has a U-shaped cross section and comprises a pair of support plates 9a, 9b that are separated from each other on both sides of the center axis of this yoke 3, and a connecting section 10 that connect one of the ends of each of these support plates 9a, 9b (bottom ends in FIGS. 13 and 14). The inner surfaces of this pair of support plates 9a, 9b become support surfaces 11 that are parallel to each other. Also, through holes 12a, 12b that are concentric with each other are formed in the sections near the other ends of these support plates 9a, 9b (top ends in FIGS. 13 and 14).
On the other hand, the cross-sectional shape of at least the tip end of the shaft 7 that is joined to the yoke 3 constructed as described above is an oval shape as shown in FIG. 13. In other words, on the outer surface on the tip end of this shaft 7 there is a pair of outside flat surfaces 13 that are parallel with each other and that are supported surfaces. Also, a notch 14 is formed in the part near the tip end on the surface of one side of the shaft 7 (top side surface in FIGS. 13 and 14) in a direction that runs parallel with both of these outside surfaces 13 (vertical direction in FIGS. 13 and 14).
When the tip end of the shaft 7 is joined to the base end 8 of the yoke 3, first, as shown by the solid line in FIG. 12, the tip end of the shaft 7 is placed on the opening side of the base end 8. From this state, by rotating the yoke 3 around the cross shaft 4 from the state shown by the solid line in the figure to the state shown by the dashed line, the tip end of the shaft 7 is inserted inside the base end 8 of the yoke as shown in FIG. 13. In order to make it easier to perform this kind of insertion work, when the yoke 3 and shaft 7 are in the free state, the space W11 between the support surfaces 11 is greater than the space W13 between the outside flat surfaces 13 (W11>W13). Therefore, when the tip end of the shaft 7 is inserted inside the base end section of the yoke 3 as was described above, a positive clearance 15 occurs between the support surfaces 11 and the outside flat surfaces 13.
After the tip end of the shaft 7 has been inserted inside the base end section 8 of the yoke 3 as described above, next, as shown in FIG. 14, a support bolt 16 is inserted through the through holes 12a, 12b, and of the male screw section 32 formed on the tip end of this support bolt 16, a nut 17 is screwed onto the portion that protrudes to the outside from the through hole 12b, and this nut 17 is tightened to a specified torque. By doing this, the space between the pair of support surfaces 11 is narrowed, and these support surfaces 11 come in contact with the outside flat surfaces 13. Together with this, by turning the support bolt 16 such that the outer surface of a cam section 18 formed in the middle of this support bolt 16 presses against the bottom surface 19 of the notch 14, the shaft 7 is pressed against the inside surface 20 of the connecting section 10. In other words, of the other surface of the shaft 7 that is parallel with the outside flat surfaces 13 (surface on the bottom side in FIGS. 13 and 14), the opposing surface 21 located on the tip end of the shaft 7 that faces the inside surface 20 of the connecting section 10 comes into strong contact with this inside surface 20. Furthermore, by fitting the support bolt 16 with the notch 14, even when the nut 17 may come loose, it prevents the shaft 7 from coming out in the axial direction from inside the base end section 8.
Of the rod section of the support bolt 16, cylindrical sections 33a, 33b are formed on the portions that are inserted through the through holes 12a, 12b and that are in the middle section and the base end section of the rod section. Also, the areas of contact between the outer surfaces around these cylindrical sections 33a, 33b and the inner surfaces of the through holes 12a, 12b are such that they support the reaction force when the outer surface around the cam section 18 is pressed against the bottom surface 19 of the notch 14. In the case of the example shown in the figures, in addition to the cylindrical section 33b, the male screw section 32 is also inserted through the through hole 12b. Therefore, in order that the outer surface around this cylindrical section 33b comes in contact with the inner surface of the through hole 12b, the outer diameter D33b of the cylindrical section 33b is nearly the same as or a little greater than the outer diameter d32 of the male screw section 32 (D33b≧d32).
In the case of the joint section between the shaft 7 and yoke 3 as described above, from the aspect of sufficiently maintaining the strength of this joint section, it is preferred that both the support surfaces 11 come in contact with the entire surface of the outside flat surfaces 13. However, when tightening the nut 17 to a specified torque as described above in order to complete this joint section, the amount that the space between the support surfaces 11 is narrowed becomes greater in the section near the support bolt 16 and nut 17 (top side section in FIG. 14), and becomes less in the section far from the bolt 16 and nut 17 (bottom side section in FIG. 14). Therefore, when the joint section is completed, in many cases, as shown in FIG. 14, the support surfaces 11 and outside flat surfaces 13 come in contact only in the portions near the support bolt 16 and nut 17, and clearances 15 remain in the portions far away.
As a result, there is a possibility that vibration will occur in the joint section while driving due to the clearances 15. In other words, in the case of the conventional joint section described above, both the inside surface 20 of the connecting section 10 and the opposing surface 21 of the shaft 7 are partial cylindrical surfaces (the contour lines (cross-sectional shapes) projected on virtual planes that are orthogonal to the axial direction are simple arcs). Also, the radius of curvature R20 of the inside surface 20 is nearly equal to or a little greater than the radius of curvature R21 of the opposing surface 21 (R20≧R21), Therefore, as shown in FIG. 13, in the state before the nut 17 is screwed onto the support bolt 16 and tightened, the shaft 7, whose opposing surface 21 is in contact with the inside surface 20, is able to rotate around its center axis O7 (within the range of the clearances 15) without the center axis moving in the upward direction in the figure. Therefore, as shown in FIG. 14, even when the shaft 7 is prevented from moving in the upward direction of the same figure by tightening the nut 17, when a large transmission torque is applied to this shaft 7 and yoke 3, the shaft 7 rotates around its center axis O7 (within the range of the clearances 15) due to elastic deformation of the components, and there is a possibility that vibration will occur inside the joint section. This kind of vibration gives the driver operating the steering wheel a noise or vibration, and a feeling of rigidity when operating the steering wheel becomes poor and is not desirable.
Also, in the case of the joint section described above, as shown in FIG. 15, due to errors in manufacturing, the bottom surface 19 of the notch 14 formed near the tip end section of the top surface of the shaft 7, may become an inclined surface with respect to a virtual plane that is orthogonal to the pair of outside flat surfaces 13. In this case, as shown in the same figure, only part of the outer surface around the cam section 18 of the support bolt 16 will come in contact with the bottom surface 19 (in the example shown in the figure, only the left end comes in contact), and a wedge-shaped clearance 22 occurs between the outer surface around the cam section 18 and the bottom surface 19. As a result, the effect of preventing rotation of the shaft 7 by the outer surface around the cam section 18 is reduced, and as described above, it becomes easy for the shaft 7 to rotate around its own center axis O7 (refer to FIG. 13) (within the range of the clearances 15).
Also, Patent Document 2 mentioned above and Patent Document 3 (U.S. Pat. No. 5,358,350), disclose construction such as shown in FIG. 16 in which the inside surface 20a of the connecting section 10a of the base end section 8a of the yoke 3a is a flat surface that is parallel with the center axis of the through holes 12a, 12b. In this second example of prior construction, in addition to the conditions of the first example of prior construction shown in FIG. 15, in the state before screwing the nut 17 onto the support bolt 16 and tightening it (not shown in the figure), the shaft 7, whose opposing surface 21 comes in contact with the inside surface 20a of the connecting section 10a, is able to move (within the range of the clearances 15) along this inside surface 20a in a displacement direction only in the axial direction of the through holes 12a, 12b (direction of the space between the pair of support plates 9a, 9b, or the left and right direction in FIG. 16). Therefore, in the case of this second example of prior construction, even when the shaft 7 is prevented from moving in the upward direction in the same figure by tightening the nut 17, it is possible for the shaft 7 to move in just the axial direction of the through holes 12a, 12b (within the range of the clearances 15) due to the elastic deformation of each of the parts. Therefore, the possibility of vibration occurring in the joint section is greater than in the case of the first example of prior construction described above, by the amount that this kind of possibility adds.
Moreover, Patent Document 2 mentioned above discloses construction such as shown in FIG. 17 in which the cross-sectional shape of the shaft 7a and the cross-sectional shape of the inner surface of the base end section 8b of the yoke 3b are both trapezoidal. As in the case of the first and second examples described above, in the case of this third example of prior construction as well, when the joint section is completed, of the space between both support surfaces 11 and both outside flat surfaces 13, clearances 15, may still remain in the areas far from the support bolt 16 and nut 17 (bottom areas in the same figure). Also, a wedge-shaped space 22 may occur between the surface around the cam section 18 of the support bolt 16 and the bottom surface 19 of the notch 14, and due to this, part of the opposing surface (flat surface) 21a of the shaft 7a may come in contact with the inside surface (flat surface) 20a of the connecting section 10a (in the example shown in the figure, only the left end comes in contact), so a wedge-shaped space 23 may also occur between this opposing surface 21a and inside surface 20a. Therefore, in the case of this third example of prior construction as well, it becomes easy for the shaft 7 to move on the inside of the base end section 8b (within the range of the clearances 15) in proportion to the amount that these wedge-shaped clearances 22, 23 exist, so there is a possibility that vibration will occur in the joint section.
Patent Documents 4 and 5 (U.S. Pat. No. 5,090,833 and EU Patent Application No. 309,344) also disclosed other examples of prior art related to this invention.                [Patent Document 1] JP Patent No. 3531364        [Patent Document 2] U.S. Pat. No. 4,900,178        [Patent Document 3] U.S. Pat. No. 5,358,350        [Patent Document 4] U.S. Pat. No. 5,090,833        [Patent Document 5] EU Patent Application No. 309,344        